We report the results of searches for B+→J/ψη′K+ and B0→J/ψη′KS0 decays, using a sample of 388×106 BB̄ pairs collected with the Belle detector at the Υ(4S) resonance. No statistically significant signal is found for either of the two decay modes and upper limits for the branching fractions are determined to be B(B+→J/ψη′K+)<8.8×10-5 and B(B0→J/ ψη′KS0)<2.5×10-5 at 90% confidence level. © 2007 The American Physical Society.